1. Field of the Invention
This invention relates to measuring apparatus for a non-contacting measurement of dimensions and/or positions of objects and/or clearances between objects, particularly workpieces, in dependence on the incidence of a laser beam on a laser beam detector, comprising a scanner for moving a laser beam emitted by a laser and projected from one edge of a measuring area across said area in a plane which is defined by said laser beam and the direction of the movement imparted to the laser beam by the scanner, and a receiver for receiving the laser beam which has been projected across the measuring area, which receiver comprises a detector, which is responsive to the incidence and non-incidence of said laser beam and controls a measuring circuit.
2. Description of the Prior Art
Measuring apparatus of that kind can be used to measure the absolute dimensions of objects which are scanned with the laser beam, also for a measurement of tolerances, for checking the roundness of rotating workpieces, for a determination of configurations and for a measurement of wear. Such measuring systems have also been used to detect the position of objects and the clearances between at least two objects.
In all known measuring apparatus of the kind discussed here, the means for moving the laser beam that has been emitted by the laser are basically identical or similar and comprise reflectors, which are disposed in the optical path of the laser beam and to which a pivotal or rotational movement is imparted by mechanical means. Such reflectors may consist of oscillating mirrors or oscillating reflecting prisms or of polyhedral prisms which have totally reflecting outside surfaces and to which a rotation is imparted so that they deflect the laser beam through a varying angle. The laser beam to which a pivotal movement is thus imparted is incident on a focussing optical system having a focus on the moving surface of the reflector so that the laser beam leaving that optical system is parallel to the optical axis of that optical system. A corresponding focussing optical system is associated with the receiver and a photodetector is disposed at the focus of the latter optical system. The time for which the moving laser beam casts a shadow of an object being scanned, so that the laser beam is not incident on the detector, is determined and is utilized for a calculation, e.g., of the diameter of said object.
The known apparatus are highly expensive because the diameter of each of the focussing optical systems must be at least as large as the width of the range being scanned. As even a strongly confined laser beam will have a finite diameter, the reflector or rotating mirror cannot be disposed at the focal point of the focussing optical system throughout the area on which the laser beam is reflected. Where mirrors are used, the thickness of the layer which must be penetrated by the laser beam until it is incident on the reflecting layer will vary with the angular position of the mirror and this will also result in a variation of the results. For this reason the focussing optical system must be corrected in each individual measuring apparatus in adaptation to the reflector which is actually used so that the scanning beam leaving the focussing optical system will be parallel to the axis of the focussing optical system even when the laser beam is scanning the measuring area near its edge. For the reasons stated above, the known measuring apparatus of the kind just described have only a narrow field of application and the determination of the result of measurement by a processing of the signals which have been generated in response to the scanning can be performed only by a computer which involves a substantial logic circuitry. In that processing, the time of non-incidence, the position of the reflector at the time of the transition between incidence and non-incidence, and other parameters, including also the instantaneous angular velocity, must be taken into account. For special purposes, the comptuer may have memories associated with it in which the measured values which correspond to predetermined combinations of parameters are stored so that it will be sufficient to retrieve said measured values for the actual measurement. But the writing of the required information into such memories is a time-consuming work and a given measuring program can be used only to perform predetermined measuring tasks.